feat(spans): Indexed spans for aggregate span waterfall (#69016)

Switch to using indexed spans instead of nodestore after a certain
cutoff date (it's when the bloom filter index on transaction name was
added to spans dataset)

I'm going to follow up with proper tests for indexed spans since these
tests were written before we had a way to store them for tests

Author: shruthilayaj

src/sentry/api/endpoints/organization_spans_aggregation.py

@@ -1,7 +1,7 @@
 import hashlib
 from collections import defaultdict, namedtuple
 from collections.abc import Mapping
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Any, Optional, TypedDict
 
 import sentry_sdk
@@ -22,6 +22,7 @@
 from sentry.utils.snuba import raw_snql_query
 
 ALLOWED_BACKENDS = ["indexedSpans", "nodestore"]
+CUTOVER_DATE = datetime(2024, 3, 22, tzinfo=timezone.utc)
 
 EventSpan = namedtuple(
     "EventSpan",
@@ -336,31 +337,29 @@ class OrganizationSpansAggregationEndpoint(OrganizationEventsEndpointBase):
     }
 
     def get(self, request: Request, organization: Organization) -> Response:
-        if not features.has(
-            "organizations:starfish-aggregate-span-waterfall", organization, actor=request.user
-        ):
+        if not features.has("organizations:spans-first-ui", organization, actor=request.user):
             return Response(status=404)
 
         try:
             params = self.get_snuba_params(request, organization)
         except NoProjects:
             return Response(status=404)
 
+        start = params["start"]
+        if start and start < CUTOVER_DATE:
+            backend = "nodestore"
+        else:
+            backend = "indexedSpans"
+
         transaction = request.query_params.get("transaction", None)
         http_method = request.query_params.get("http.method", None)
         if transaction is None:
             return Response(
                 status=status.HTTP_400_BAD_REQUEST, data={"details": "Transaction not provided"}
             )
 
-        backend = request.query_params.get("backend", "nodestore")
         sentry_sdk.set_tag("aggregate_spans.backend", backend)
 
-        if backend not in ALLOWED_BACKENDS:
-            return Response(
-                status=status.HTTP_400_BAD_REQUEST, data={"details": "Backend not supported"}
-            )
-
         query = f"transaction:{transaction}"
         if http_method is not None:
             query += f" transaction.method:{http_method}"